Smaller internal combustion engines have been popular for decades for powering pumps, grass-cutting equipment, pressure washers, standby generators and the like. Earlier in the history of such engine usage, there was little concern about pollution such as exhaust emissions. But the number of smaller engines in use has increased dramatically and concurrent steps were and are being taken by engine manufacturers and state and federal regulators to help assure that air pollution of engine origin is minimized. A particular emission standard is promulgated by the California Air Resources Board (CARB).
One way to limit pollution while yet obtaining rated or near-rated horsepower out of the engine is to feed fuel to the engine at a particular rate or at a rate which is within a narrow range of rates. When an engine is to be fueled by a single liquid or gas fuel having a known, standard energy content per unit of fuel measure, e.g., British Thermal Units (BTU) per pound, it is a relatively straightforward task to configure a valve to flow fuel from a source to the engine at a particular rate.
But the matter of engine fueling while yet meeting emission standards becomes more complex when an engine is to be fueled with either of two fuels such as natural gas (NG) or liquefied propane gas (LPG). This is so since while LPG has a known, standard energy content per unit of fuel measure, natural gas does not. The energy content of natural gas can and does vary about plus or minus 10% from some norm. Therefore, when fueling a small engine, it is necessary (to meet certain regulatory standards) to be able to adjust the fuel flow rate to obtain high engine horsepower and still stay within the limits established by such standards.
While not particularly relevant to engine fueling, the two-port radiator valve disclosed in U.S. Pat. No. 1,015,164 (Fowden) uses two stops with the valve "off" position about midway between the stops. When the valve indicating finger is against one stop, a reduced-area flow path is established through the valve. And when the valve is turned through "off" to the second stop, a larger-area flow path is established.
U.S. Pat. No. 914,209 (Watson), U.S. Pat. No. 1,104,918 (Mouat), U.S. Pat. No. 2,010,201 (Ruttiman) and U.S. Pat. No. 4,815,693 (James et al.) disclose the idea of using stops to limit the degree to which a valve is opened or closed. For example, the James et al. patent discloses using two pins which stop valve handle travel at the fully open and fully closed positions, respectively.
None of the aforementioned patents relate to engine fueling or recognize the problem addressed and resolved by the invention. Nor do any of the aforementioned patents suggest configuring a valve to be tamper-resistant. This is not surprising--certain of the valves disclosed in such patents are intended for use with steam radiators or in other applications where the ability to adjust the valve over a wide range is important.